1. Field of the Invention
The present invention relates to a novel dental resin sheet which is veneered onto the surface of a tooth or onto the crown to form the surface layer of the tooth or the crown.
2. Description of the Related Art
Rigid plastic shells have been widely used to cover teeth in a dental prosthetic treatment. In an actual treatment, a shell of which surface is beforehand shaped to match the surface a tooth is used; bonding agent is applied onto the surface of the tooth; and the shell is then attached onto the tooth after dental cement is plastered onto the tooth. Although the hard shell has beforehand been shaped to the tooth, the shell is usually unable to perfectly match the configuration of the tooth when it is attached, and thus, the shell would leave some gap between the inner surface of the shell and the outer configuration of the tooth. The cement is thus required to fill the gap.
During a dental treatment session, a patient is continually subjected to stress such as pains or mouth openings for treatment. Thus, the shorter the session, the better. Cement is available to fill the gap between the inner configuration of the shell and the tooth. The shell outer configuration, however, does not always match the original shape of the tooth that has had an intimate functional cooperation with other tooth in the patient mouth for a long time. With the shell, it is subjected to grinding and polishing. Such a treatment is sometimes time-consuming, and puts the patient under physical and metal pressure. Furthermore, the grinding and polishing operation can change the original shading of the shell.
In the production of a resin veneering crown, it is important to use resin that closely simulates the shading of the natural teeth of the patient. Ten or more shade guides are currently available. From among them, a shade guide that is near to the shading of the patient teeth is picked out. Each guide is numbered, and the number of the selected guide is referenced to select paste resin. In a commonly practiced procedure, opaque is applied onto the surface of the metal crown, and then an instrument is used to plaster resin onto opaque covered crown. In the final step, the resin is subjected to light for a certain period time if it is a lightcuring resin, and is heated for a certain period of time if it is a heat-curing resin. This concludes the production of the resin veneering crown.
The color of natural teeth is not uniformly shaded, but varied from location to location; for example, cervical, dentin and incisal are different in shading. Furthermore, the thickness of each tooth layers affects the surface shading. Furthermore, the shading of the tooth varies from person to person, and also with age. Thus, rather than a single type resin with a single shade, two to four resins with different shadings are used and prepared on a case-by-case basis so that the resulting shade may be as natural as the shading of the patient teeth.
In practice, however, matching faithfully the selected shade guide is a difficult task. Simulating accurately the natural shading and even surface irregularity of the tooth requires quite a lot of experience. Thus, difference in level of skill in dental technicians who have prepared crowns affects greatly acceptability of each crown. Thus, no uniform quality is assured.